This program project combines contemporary immunologic and epidemiologic approaches to study the pathogenesis and natural history of three emerging viruses: Lassa fever virus, Ebola virus and Sin Nombre virus. In Project 1 the identity of peptide epitopes for Lassa specific CTL responses in humans will be sought by application of predictive computer algorithms to select 9 and 10 mer epitopes from the sequences of the Lassa N and GPC genes. Peptides will be selected for synthesis and assessed for capacity to bind at high affinity to MHC class 1 molecules. Those showing high affinity binding activity will be further tested for capacity to serve as CTL epitopes in 51Cr release assays using peripheral blood lymphocytes obtained from Lassa seropositive donors in West Africa. It is anticipated that this analysis will provide a clear view of the diversity and specificity of human CTL activity against this important arenavirus Project 2 will utilize recombinant phage display techniques to generate panels of human antibodies to Ebola and Hantaviruses from seropositive individuals. The unique strengths of this technology are a) the ability to select possibly rare but highly potent human antibodies and to evolve these antibodies in vitro to be still more effective, and b) the ability to exquisitely target selection to yield broad reactivities across a wide variation in virus phenotypes. The antibodies generated in this project will find application as immunoprophylactic and immunotherapeutic reagents and will also be useful in guiding vaccine design and as advanced analytical reagents for field studies. Project 3 will investigate why Sin Nombre virus (SNV) has a relatively high rate of endemic infection in Peromyscus spp., but a low incidence of exposure in high risk human populations. Factors to be investigated include virus strain variation, genetic differences within the genus Peromyscus, pathogenesis of the virus in Peromyscus and ecological factors affecting the incidence of infection. Biological and immunologic properties of SNV variants isolated from humans and Peromyscus spp. will be compared. Antibodies from rodents, humans and a human antibody expression library (Project 2) will be tested for virus neutralization (plaque reduction) using SNV variants. Pathogenesis studies will be conducted using in situ hybridization and immunochemistry to determine the distribution of virus in tissues of naturally infected Peromyscus. Ecological factors affecting transmission of the virus in native rodents will be a collaborative study with Project 4. GIS and remote sensing will be used to identify ecological factors important in maintenance of hantaviruses. The Desert Research Institute and the Biology Department at the University of Nevada will use vegetation, soil and usage maps of the Walker River Basin (California and Nevada) to analyze the distribution of SNV in native rodents (provided by Project3). This information will be used to develop a model of the ecology of SNV in native rodents to be used for large scale predictability of the distribution and incidence of SNV.